It's a term for a type of emotional abuse, coined in reference to an old film which I think was called Gas Light. The abusive husband in the film wants shot of his wife, so starts gradually turning down the gas wall lights in the house a tiny bit at a time. When his wife comments that it seems to be getting dimmer, he claims there is no difference, its all in her head, maybe she is imagining things etc. I think he tries to get her packed off to the mad house in the end.

It is often used as a short hand for someone who is EA and manipulative in that they do things then deny then to make their partner question their own sanity. I believe it is a quite common 'technique' used to control partners by diminishing their ability to trust their own judgement.

She told me she wouldn't be able to divorce him and I thought it couldn't be right that they'd leave abuse survivors to drag it out so I had a Google but we couldn't see how she could prove it. She's almost feeling bad she moved in with friends rather than going to a shelter, but she has twin toddlers so of course she wanted to take her friends up. All of her friends have seen what she's been through and the change in her since.

My friend has just left her husband who is a gaslighter. She can't afford to divorce and we were looking at the legal aid rules but found them confusing. It looks like she should be able to get it but the evidence it says seems to only apply to physical abuse. It's obviously not something she needs dragging out. Does anyone know if or how you can prove mental abuse?